The U.S. Transportation Security Agency announced additional restrictions for carry-on items aboard Russia-bound flights, just hours before the Winter Games are due to begin in Sochi. The heightened security measure comes a day after the U.S. government warned that terrorists might try to smuggle explosives-making materials aboard commercial planes hidden in toothpaste tubes. Security officials worry that terrorists could use ingredients disguised in these kinds of items to assemble makeshift bombs aboard a plane, a senior U.S. official told ABC News.

The U.S. Department of Homeland Security did not warn of any specific threat in a statement to the media, but said that it "will continue to respond and appropriately adapt to protect the American people." 

Delta Airlines, which operates daily flights from the U.S. to Moscow, released a statement on its website, saying that the TSA directive banned "liquids, gels, aerosols and powders of any size." Delta also said that all customers traveling on its flights to Russia would not be allowed to use their mobile devices or airport kiosks to check in. Passengers instead will need to meet with airline representatives at the airport prior to departure.

Beginning in January, Russia banned almost all liquids in airline carry-on luggage at all the country's airports. This came after suicide bombings in the city of Volgograd that killed 34 and injured more than 100 in three separate attacks in December. Militants in Russia's restive Caucasus region called for attacks on the Sochi Olympics beginning in the summer of 2013.

In an interview with NBC, President Obama said, "I think the Russians have an enormous stake, obviously, in preventing any kind of terrorist act or violence at these venues. They have put a lot of resources into it." adding, "We're in constant communications with them."

Declaring Russia "ready to host the Games," President Vladimir Putin called the preparations in Sochi "a huge project... the biggest construction site in the world."

Russia has deployed an astonishing 100,000 security personnel to the Black Sea resort city, according to U.S. security consultant Stratfor, four times the number assigned to the 2012 Summer Games in London. Russia is estimated to have spent $51 billion on the event, beating out the 2008 Summer Games in Beijing as the most expensive Olympics on record.